The invention relates to the manufacture of expandable cylindrical metal meshes for use in expandable stents and in particular to the customized manufacture of expandable metal stents.
A cardiologist performing a stent implant procedure requires several stents of various geometrical shapes and lengths in order to be able to quickly choose an optimal stent during the surgery. Depending on the location and degree of damage being repaired, the cardiologist may need as many as eight different pattern stents with lengths ranging from about 6 mm to about 40 mm. During surgery, the cardiologist may have as little as five minutes to select the proper stent. Therefore, hospitals and clinics performing these procedures generally have a substantial number of stents on hand, perhaps as many as 40 or more, for use with a single patient. Given the relatively high cost of stents and their consumption, hospital and clinic expenditures on such operations may be substantial. As a result, many hospitals and clinics without adequate financial resources do not perform surgical procedures involving stent implantation.
There exists, therefore, a need for a system that reduces the number of costly stents required during surgical procedures by allowing a surgeon or clinic staff to select and fabricate a custom stent during a surgical procedure and within a short period of time.
Methods that have previously been used to manufacture stents are described in U.S. Pat. Nos. 4,856,516, 4,907,336, 5,116,365, 5,135,536, and 5,707,386. Stents produced by the methods disclosed therein contain bent wires that are knotted, which introduces stresses into the metal and decreases the quality of the stents. Moreover, these stents are not generally suitable for curved portions of blood vessels. More importantly, these methods only produce stents with a configuration that is tailored to a specific surgical instrument, limiting their usefulness. Other methods that have been used to manufacture stents are described in U.S. Pat. Nos. 5,725,548 and 5,907,893. Stents produced by the methods disclosed therein are joined along a line longitudinal to the length of the stent and then welded. However, at the high temperatures required to weld these joints, the crystalline structure of the metal can be affected and thereby reduce the reliability and strength of the stent and its compatibility in a biochemical environment.
Still other methods of manufacturing stents are described in U.S. Pat. Nos. 4,383,896, 4,496,434, 5,030,329, 5,328,587 and 5,772,864. Stents produced by the methods disclosed therein are free from wire knots and welded joints. They are produced using an electrochemical process, which generally produces higher quality stents. However, the methods disclosed, most notably in U.S. Pat. No. 5,772,864, are complex and time consuming. For example, grooves outlining the stent must be etched on very small mandrels with instruments requiring precise control. Then, the cleaned mandrel must be dipped in an electrochemical bath containing a selected metal for up to approximately 12 hours. The stent material must then be carefully removed and further processed and polished. Because the entire process is costly and time consuming, it is not appropriate for use in a hospital or clinical setting during a shunting procedure.
Still other methods of manufacturing stents are described in U.S. Pat. Nos. 4,733,665, 4,776,337, 5,421,955 and 5,514,154. Stents produced by the methods disclosed therein are made using laser technology to directly carve the geometrical contours of stents on tubular blanks. Manufacturing of stents by these methods is associated with formation of sharp edges and burrs on the outside and inside surface of the stent. This can affect the structure of the stent, thereby reducing its reliability. This also requires additional processing to remove these undesirable features. Moreover, the cost and complexity of this technology can limit its use in hospital and clinical settings.
A solution to some of these problems is disclosed in U.S. Pat. No. 5,421,955, where laser technology is used to form a pattern on a mask material that is subsequently etched in an electrochemical process. However, this process requires complex instruments for precise laser control, an etching bath and solution, and extended processing time that may prohibit its use in a hospital or clinical setting.
A proposed solution to the above mentioned problems is disclosed in U.S. Pat. No. 5,902,475 in which much of the stent processing may be carried out prior to its use in a surgical procedure, with the final processing done in the hospital or clinical setting. For example, a tubular blank is coated with a photoresistive polymer over a photo film that contains a stent pattern. It is mounted on a rotatable tube and exposed to ultraviolet rays, thereby creating a negative image of the stent. The film is developed such that the illuminated lines solidify. The film is then placed in an electrochemical bath and the non-illuminated surfaces dissolve. The steps of blank mounting and removing can require up to a total of approximately six minutes to accomplish. The step of transferring and immersing the blank in the electrochemical tank can require up to approximately ten minutes. The step of electrochemically removing the non-illuminated areas can require up to approximately six minutes, with the final step of polishing/processing taking up to approximately 3 minutes. In total, the process described in U.S. Pat. No. 5,902,475 takes about thirty minutes, limiting its usefulness during surgical procedures. Moreover, this process requires, for certain applications, use of cathode made from platinum, gold or their alloys to withstand the strong acidic electrolyte solutions, phosphoric or sulfuric acid. Additional processing steps to prepare the stent for subsequent use may also be required. It is apparent that the additional expense and hazards associated with this method prohibit its use in hospital or clinical settings.
Stents produced by the methods described in U.S. Pat. Nos. 5,421,955, 5,772,864 and 5,902,475 rely on technology that prevents production of high quality stents. For example, the inner surface structure of the holes in the base stent tubes may be nonhomogeneous after the electrochemical treatment, e.g., includes sharp edges, protrusions, etc. Under certain conditions, the stent blank could become contaminated with impurities such as oxides or include other defects. Under these conditions, current supplied to the blank during processing would not be uniform. Further, an additional step is required to process the inner surface of the stent holes. Therefore, it would be desirable to apply the electric current to the external surface of the stent blank during processing rather than the inner surface.
Additionally, the known manufacturing methods may require the use of a diamond dust polishing tool to treat not only the external surface of the final stent but also the internal surface area. This additional step adds to the cost and complexity of the manufactured stent.
Accordingly, prior to the present invention, there have been no described methods of manufacturing stents: that allow surgical or clinical staff to fabricate custom stents as an integral part of the surgical procedure; that require relatively few complicated instruments or dangerous chemicals, that is relatively inexpensive; and that produces stents free from thermal stresses, sharp edges or surface irregularities.
In accordance with the present invention, a method and device for manufacturing and implanting an expandable stent into a body lumen is carried out by electrochemically forming the expandable stent just prior to implantation. The electrochemical forming includes providing a cathode which includes a pattern for producing the stent; providing a tubular blank adjacent to the cathode; delivering an electrolyte between the cathode and the tubular blank; relative displacing the tubular blank and the cathode; and, electrochemically producing the stent with the stent pattern for subsequent implantation.
Other features of the invention include using a tubular blank that has a diameter and thickness equal to the stent to be manufactured; cutting the ends of the tubular blank after the stent outline is formed; using a mandrel for receiving the tubular blank, in which the mandrel has a linear slit along its longitudinal length parallel to the tubular blank for the introduction of electrolyte and wherein the linear slit is narrower than the diameter of the tubular blank; removing an insulating coating on the cathode before electrochemically forming the stent; customizing the expandable stent according to the needs of a patient being treated; and implanting the stent into a body lumen.
Still other features include electrochemically forming at a current density of about range 50 A/cm2, or more; delivering the electrolyte at a velocity of from 8 m/s to 10 m/s; and displacing the blank by centerless rotation.
Also disclosed in a method of custom-forming an expandable stent in an operating or emergency room during a procedure to implant the stent into a body lumen of a patient, including providing a plurality of cathodes, at least some of which includes a different stent pattern, mounting the cathodes on a rotator; providing a plurality of tubular blanks, at least some of which includes a different material, diameter and thickness; selecting working cathode with a desired stent pattern; selecting a stent blank from the plurality of tubular blanks; mounting the stent blank in an operative relationship to the working cathode; rotating the rotator while delivering an electrolyte between the desired stent pattern and the stent blank to electrochemically form the stent having the desired stent pattern; and recovering and preparing the recovered stent for implantation into the patient""s body lumen.
Other features of the invention include using a mandrel for receiving the stent blank, in which the mandrel has a linear slit along its longitudinal length parallel to the stent blank for the introduction of electrolyte and wherein the linear slit is narrower than the diameter of the stent blank; removing an insulating coating on the plurality of cathodes before electrochemically forming the stent; electrochemical forming at a current density of about range 50 A/cm2, or more; cutting the ends of the electrochemically-formed stent outline; delivering the electrolyte at a velocity of from 8 m/s to 10 m/s; and rotating the tubular blank by centerless rotation.
Also disclosed is an apparatus for custom-forming an expandable stent in an operating or emergency room during a procedure to implant the stent into a body lumen of a patient for implantation into a body lumen, which includes a rotator, for carrying one or more cathodes; a mandrel positioned parallel to the rotational axis of the rotator, for holding a tubular blank in operative relationship to the working cathode which is currently employed for custom forming; a conduit for delivering electrolyte to the working cathode and the tubular blank; means for simultaneously rotating the rotator and the tubular blank; and means for supplying electrical voltage to the working cathode and to the tubular blank to produce a stent.
Other features of the apparatus aspects of the invention may include a grinding means for removing an insulating coating from the cathodes; means for separating the working cathode with the desired stent pattern and the tubular blank by a distance of not more than 0.05 mm; a mandrel with a linear slit directed parallel to the length of the tubular blank for the delivery of the electrolyte between the working cathode and the tubular blank and wherein the linear slit is narrower than the diameter of the tubular blank; one or more cathodes being made from a metal selected from the group consisting of gold, platinum, stainless steel, brass, copper, or alloys thereof; and a tubular blank that has a diameter and thickness equal to the stent.
Another feature of the invention include a housing for containing therein the mandrel, the rotator, the tubular blank, the one or more cathodes, and the conduit and wherein the housing is positionable in an area substantially near a patient being treated for a stent implant.
Still other features of the invention include a lateral support comprising two pairs of tubular rests, the pairs of tubular rests each containing longitudinal slits, for supporting the tubular blank in the mandrel in an operative relationship to the working cathode, and a means for self-aligning the mandrel in operative relationship to the working cathode.
These and other objects, advantages and features of the invention will become better understood from a detailed description of the preferred embodiment of the invention, which is described in conjunction with the accompanying drawings.